System and Method for Concrete Slab Connection

ABSTRACT

Systems and methods of transferring loads between adjacent cast-in-place slabs, such as concrete slabs, and for accurately positioning dowels between adjacent sections of slabs are provided. A generally planar plate-type dowel is used which may be positioned within a cutaway in a preexisting slab of concrete. The dowel is shaped to generally conform to the shape of the cutaway, which is made by a saw blade. Once the dowel is positioned within the preexisting slab, a new slab is poured adjacent the preexisting slab. Rubber seals are included on the edges of the dowels to provide spacing or a gap between the dowel and the preexisting slab to allow for lateral independent movement of the adjacent slabs, and to prevent concrete from the newly poured second slab from entering into the gap. A saw unit for making a generally planar cut horizontally into an edge of a hardened concrete slab is also provided.

This application is a divisional application of U.S. patent applicationSer. No. 11/150,403, which claims priority pursuant to 35 U.S.C. 119(e)to co-pending U.S. Provisional Patent Application Ser. No. 60/578,512,filed Jun. 10, 2004, the entire disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present inventions relate generally to systems and methods forpavement reinforcement. More particularly, the present inventions areconcerned with systems and methods of transferring loads betweenadjacent cast-in-place slabs, such as concrete slabs, and for accuratelypositioning dowels between adjacent sections of slabs.

BACKGROUND OF THE INVENTION

In the construction of concrete floors or surfaces (i.e. sidewalks,driveways, roads, etc.), it has long been the practice to make thesurface from a series of individual blocks or slabs. Adjacent slabs meeteach other at joints which are typically spaced so that each slab hasenough strength to overcome internal stresses that would otherwise causerandom stress relief cracks.

One problem that can arise when slabs are poured in separate subsectionsis that the junctions or joints between adjacent sections are subject todamage from downward forces exerted against the slab. To reduce theeffects of such forces, it is common practice to embed dowels into theslab. The dowels bridge across the joint between adjacent subsections ofthe slab and extend a short distance into each subsection. The dowelsare placed at regular intervals along the joint, and act to equalize andtransfer loads that are exerted against the joint. Various systems havebeen developed utilizing dowels of a variety of shapes and sizes,including generally planar plate-type dowels, as well as dowels havingsquare, circular or other shaped cross-sections.

If the dowels are not installed correctly, problems can arise.Specifically, if the dowels are not parallel to the slab surface andperpendicular to the joint between the slab sections, unwanted stressescan be created in the slab, which can lead to cracking of the slab. Anumber of systems and methods have been developed to better ensureproper alignment of the dowels. In some systems dowels, or sheaths forsupporting the dowels, are attached to forms prior to pouring of aconcrete slab. For example, in U.S. Pat. No. 6,354,760, the disclosureof which is incorporated herein by reference in its entirety, agenerally planar plate-type dowel is shown which is supported by asheath that is embedded within one of two adjacent concrete slabs. Thesheath is nailed to an inner surface of a wood form as a first slab ispoured. Once the slab has properly hardened, the form is removed and thesheath remains. The dowel is then positioned in the sheath such thathalf of the dowel protrudes beyond the edge of the slab into a locationthat will be occupied by the adjacent slab. The adjacent slab is pouredand the protruding portion of the dowel is surrounded by the concrete ofthe second slab.

The generally planar plate-type dowels discussed above provide severaladvantages over square and round tubular dowels such as increasedrelative movement between slabs in a direction parallel to thelongitudinal axis of the joint; and reduced loadings per square inchclose to the joint, while transferring loads between adjacentcast-in-place slabs. Nevertheless, current systems and methods utilizingplanar plate-type dowels require that the dowel be installed in newconcrete as it is poured. Alternatively, systems and methods have beendeveloped in which a hole is drilled into pre-existing hardened concretefor insertion of a tubular dowel, allowing tubular dowels to be utilizedin section repair or other retrofitting applications in which theconcrete has been poured and set/hardened prior to placement of dowel(or sheath) within the slab. Notwithstanding, the noted disadvantages oftubular dowels versus planer dowels, drilling in existing concrete isextremely time consuming and creates considerable dust which isundesirable for interior retrofit applications. Therefore, it would bebeneficial to provide a system and method for utilizing planar dowels inconnection with existing or retrofit concrete applications, and which iseasier and less dusty than existing retrofit systems utilizing tubulardowels.

A disadvantage of prior art systems and methods of utilizing planardowels in new concrete pours in which a sheath is embedded in a slab, isthat only wooden forms can be used for forming the slab. This is becausethe sheath must be nailed to the form before the concrete is poured.Nevertheless, many contractors prefer to utilize reusable metal forms asopposed to wooden forms. Therefore, it would be beneficial to provide asystem and method for utilizing planar dowels in slabs that are madewith metal forms.

Utilization of the generally planar sheaths of the prior art forpositioning dowels within a slab require vibration of the wet concreteto allow the concrete to consolidate around the sheath. When theadjacent slab is poured, the wet concrete for that slab must also bevibrated to allow the concrete to consolidate around the protrudingportion of the dowel. Vibration of the wet concrete requires additionallabor and special tools that are not necessary in applications in whichgenerally narrow tubular dowels are utilized. Therefore it would bebeneficial to provide a system and method for utilizing planar dowels inslabs that reduces the labor required during pouring.

Another disadvantage of prior art systems for locating planar dowels ina slab is that attachment of the sheath to the form requires extremelycareful positioning of the sheath with respect to the top edge of theform as well as extremely careful leveling of the form at the locationin which the slab edge is to be made. Even slight misalignment of eitherthe sheath or of the form board will result in misalignment of the dowelwith the slab and can result in undesired stresses in the slab.Misalignment or dislocation of the sheaths can result after the sheathhas been mounted to the form either as the form is being positioned orafter the form is in position by workers accidentally stepping on thesheaths or bumping against the sheaths. Misalignment of the form boardcan also result from workers accidentally kicking the form board, ormisalignment can be the result of a warped form board. Therefore, itwould be beneficial to provide a system and method for ensuring properalignment of planar dowels in slabs.

SUMMARY OF THE INVENTION

An object of the instant invention is to provide a system and method fordoweling in existing concrete that is faster and cleaner than drilling.Another object of the instant invention is to provide a system andmethod for positioning planar dowels into existing concrete. Yet anotherobject of the instant invention is to provide a system and method forutilizing planar dowels with metal forms in new concrete applications.Still another object of the instant invention is to provide a system andmethod for properly aligning planar dowels in a slab. Another object ofthe instant invention is to provide a system and method for utilizingplanar dowels in a slab that minimizes the amount of labor requiredduring new concrete pours.

The objects of the instant invention are accomplished through the use ofa generally planer plate-type dowel and a machine, such as a saw, formaking a generally planar cut horizontally into an edge of a hardenedconcrete slab. One end of the dowel is shaped to generally conform tothe shape of the cut made by the saw. The size of the dowel is slightlysmaller than the size of the cut to allow slight movement generallyparallel to the edge of the slab in which the cut is located.

In operation, a first slab of concrete is either a pre-existing slabthat is being repaired, or a relatively new slab that has been allowedto set or harden. In the context of a repair application, a generallystraight edge to the existing concrete may be made by cutting away asection of the existing slab. In the context of a relatively new slab, astraight edge will be made by a form board that is removed after theconcrete has hardened. Once the concrete is hardened and/or a straightedge is obtained, a saw is used to plunge-cut into the edge of the slabat a depth midway between the top surface and the base of the slab. Thedowel is then inserted into the cut and the adjacent slab such that halfof the dowel is located within the cut in the existing slab and half isprotruding from the slab into a location in which an adjacent slab ofconcrete is to be poured. The adjacent slab is then poured and vibrationof the wet concrete of the adjacent slab is used to consolidate theconcrete around the protruding portion of the dowel.

Although vibration of the concrete is necessary for the adjacent slab,roughly half the amount of vibration-related labor is utilized inconnection with the system and method of the instant invention as isrequired by systems of the prior art. This is because vibration labor isonly utilized on the adjacent slab, as opposed to both slabs as isnecessary in the prior art systems. Cutting into an existing, hardened,slab and placement of a dowel in the cut-away, eliminates the need forvibration in the first slab.

In a preferred embodiment of the instant invention the saw isself-guided by a control unit that moves across the top of the slabfollowing the slab edge. The saw can be adjusted to provide a series ofspaced-apart cuts along the edge of the slab. In another preferredembodiment, the saw will include a mist system to eliminate dust createdas the concrete is cut. Such a system is ideal for interior use of theinventive system.

In a preferred embodiment of the instant invention rubber gaskets, orseal spacers, are connected to the dowel to aid in alignment of thedowel in the cutaway in the slab and to prevent concrete slurry frommigrating into the cutaway area in which the dowel is located as theadjacent slab is poured.

The dowel plates utilized in the instant invention can be made in avariety of shapes and sizes depending upon the desired application andthe shape of the cut into which the dowel is to be located. The shapecan include two generally symmetrical ends, one of which is positionedin the cut-away of the existing slab and the other protruding from theslab to extend into the adjacent slab when it is poured. Alternatively,the shape can be asymmetrical. If an asymmetrical dowel plate isutilized, one end will have a shape generally conforming to the shape ofthe cut that is made in the existing slab. The shape of the other endwill have little significance as the wet concrete will consolidatearound the protruding end by vibration of the concrete. The dowel platesutilized in the instant invention can also be utilized in connectionwith a mounting sheath similar to that used by systems of the prior art,allowing a single dowel to be used both for new construction andretrofit applications.

The system and method of the instant invention provides a means forpositioning planar dowels into a retrofit application that is muchfaster and cleaner than the systems of the prior art. Sawing into a slabof concrete is much faster than drilling. In addition, the use of a wetsaw device greatly reduces the amount of dust created duringinstallation. In addition, the system of the instant invention allowsthe use of any type of forms, whether wood, metal or otherwise, as thereis no need to nail sheaths to the forms prior to pouring of the slab.Furthermore, the instant invention eliminates the possibility ofmisalignment of dowels caused by improper form alignment or byaccidental dislocation of dowel mounting sheaths as the slab is poured.This is accomplished by cutting into the slab after the slab hashardened. The angle and position of the cut is gauged by the actualsurface of the slab, providing ideal alignment of the dowel with respectto the slab surface.

The foregoing and other objects are intended to be illustrative of theinvention and are not meant in a limiting sense. Many possibleembodiments of the invention may be made and will be readily evidentupon a study of the following specification and accompanying drawingscomprising a part thereof. Various features and subcombinations ofinvention may be employed without reference to other features andsubcombinations. Other objects and advantages of this invention willbecome apparent from the following description taken in connection withthe accompanying drawings, wherein is set forth by way of illustrationand example, an embodiment of this invention and various featuresthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention, illustrative of the best mode inwhich the applicant has contemplated applying the principles, are setforth in the following description and are shown in the drawings and areparticularly and distinctly pointed out and set forth in the appendedclaims.

FIG. 1 is an elevation view of a plunge-cut saw unit of the instantinvention.

FIG. 2 is a top view of the saw unit shown in FIG. 1.

FIG. 3 is a top section view of a planar dowel plate located within acutaway in an existing concrete slab through the system and method ofthe instant invention.

FIG. 4 is a side section view of the planar dowel located within acutaway in an existing concrete slab shown in FIG. 3.

FIG. 5 is a top plan view of a plastic sheath (receiver) for locating adowel plate of the inventive system into a newly poured slab of concreteas the slab is poured.

FIG. 6 is top section view of an alternative embodiment of a dowel plateof the system of the instant invention.

FIG. 7 is a top section view of another alternative embodiment of adowel plate of the system of the instant invention.

FIG. 8 shows a detailed view of a ring saw of the instant invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As required, a detailed embodiment of the present inventions isdisclosed herein; however, it is to be understood that the disclosedembodiment is merely exemplary of the principles of the invention, whichmay be embodied in various forms. Therefore, specific structural andfunctional details disclosed herein are not to be interpreted aslimiting, but merely as a basis for the claims and as a representativebasis for teaching one skilled in the art to variously employ thepresent invention in virtually any appropriately detailed structure.

Referring to FIGS. 1 and 2, a plunge-cut saw unit (10) of the instantinvention is shown. As shown in FIG. 1, saw unit 10 travels over the topof preexisting concrete slab 100 on wheels 20 following edge 110 of slab100. The height of cutting blade 18 is adjustable to control thevertical depth at which the cut is made into slab 100 by raising andlowering mechanism (not shown) which raises and lowers drive unit 14along with saw blade 18 relative to support arm 15. Alternatively, theheight of saw blade 18 may be adjustable by extending and retractingblade drive shaft 22 from blade drive unit 14. Depth stop sensor 19 isincluded to prevent the vertical depth of the cut from being made tooclose to the bottom of slab 100. As shown in FIG. 1, depth stop sensor19 is a member extending downward from drive unit 14. Depth stop sensor19 will bottom out on the ground if drive unit 14 is positioned tooclose to the ground, providing a minimum height for the plunge cut bysaw blade 18.

Saw blade 18 is plunged horizontally into edge 110 of slab 100 throughthe extension of engagement cylinder 16 and is retracted from slab 100by springs (not shown) which are positioned to provide a retractingforce on saw blade 18 when engagement cylinder 16 is in the extendedposition. In a preferred embodiment engagement cylinder 16 comprises ahydraulic piston, however it will be appreciated that alternativeengagement mechanisms may be utilized. When pressure is applied to thehydraulic piston, engagement cylinder 16, which is connected to the endof support arm 15, is extended to push drive unit 14 (as well as sawblade 18) inward on support arm 15 towards power unit 12. When pressureis released from the hydraulic piston, the force of the springs willpull drive unit 16 outwards towards the end of support arm 15 away frompower unit 12. Drive unit 14 moves horizontally along support arm 15 byriding along slide rails 13.

Power unit 12 includes a drive mechanism or motor to propel saw unit 10on wheels 20. Power unit 12 also includes control circuitry for saw unit10 including controls for saw drive unit 14, saw blade 18, engagementcylinder 16, retracting cylinder 17, and any other desired components ofsaw unit 10. Retracting cylinder 17 connects power unit 12 to supportarm 15, such that upon retraction of retracting cylinder 17 support arm15 is pivotally raised upward to raise saw blade 18 away from thesurface of slab 100 for transportation of saw unit 10. Upon extension ofretracting cylinder 17 support arm 15 is pivotally lowered toward thesurface of slab 100 into the generally parallel orientation shown inFIG. 1.

As is shown in FIG. 2, saw unit 10 includes edge guide sensors 11extending from support arm 15. Edge guide sensors 11 are designed tomaintain contact with edge 110 of slab 100 when saw unit 10 is properlyfollowing edge 110. Edge sensors 11 allow saw unit 10 to be programmedto follow edge 110 and create plunge cut at preset intervals along edge110 so that dowels 30 of the instant invention can be positioned in slab100.

Referring to FIG. 8, a detailed view of an embodiment of a motorassembly for saw blade 18 is shown. The motor assembly includes sawmotor 24 which drives drive motor 26 which in turn rotates saw blade 18.In an embodiment of the instant invention shown in FIGS. 1 and 2, sawmotor 24 is located in drive unit 14, and drive shaft 22 functions asthe drive motor.

Referring to FIGS. 3 and 4, one embodiment of an inventive dowel plate(30) as it is used in accordance with the system and method of theinstant invention is shown. FIGS. 3 and 4 show an embodiment in whichdowel 30 is positioned in a preexisting, hardened slab of concrete, 100,and then a new slab of concrete, 200, is poured adjacent to the existingslab. Cutaway 120 is made in edge 110 of slab 100. Cutaway 120 can bemade using saw unit 10 described above, or otherwise made withalternative saw units, such as ring saws of the prior art. Steel dowel30 shown in FIG. 3 has semi-circular edge which is shaped to conformgenerally to the shape of cutaway 120. Dowel 30 includes a pair ofslots, 32, for receiving and holding rubber centering seals 35 whichprotrude from dowel 30. Seals 35 function to center dowel 30 withincutaway 120 such that gap 130 is provided between the outer surface ofcutaway 120 and edge 31 of dowel 30. Gap 130 allows for lateralindependent movement of the two concrete slabs that are being joinedtogether via dowel 30 (including preexisting slab 100, and future slab200 located directly adjacent slab 100). Once dowel 30 is properlypositioned in preexisting slab 100, new slab 200 of concrete is pouredand the concrete is subjected to vibration to allow the concrete toconsolidate around to portion of dowel 30 located in new slab 200. Seals35 will prevent concrete from new slab 200 from flowing into gap 130.

Referring to FIG. 5, an embodiment of a sheath/receiver (150) similar tothat used by systems of the prior art (such as in U.S. Pat. No.6,354,760) is shown. Sheath 150 is made of a plastic, or other suitablematerial and includes inner void 151 for receiving dowel 30. In oneembodiment, spacers 152 project from the inner surface of void 151 tocreate gap 130 between dowel 30 and the slab in which sheath 150 islocated. Spacers 152 can be molded into sheath 150, or alternatively canbe separate components attached to, or otherwise associated with, sheath150. Sheath 150 also includes pre-mounted nails 170 which are driveninto slab form boards 160 to mount sheath 150 in position prior topouring of the slab. Once sheath 150 is mounted to form 160 for theslab, the slab is poured. Tape 154 covers the opening of void 151 sothat concrete will not flow into void 151 when the slab is poured. Thewet concrete is vibrated to allow the concrete to consolidate aroundsheath 150. Once the concrete has sufficiently hardened, form boards 160are removed and dowel 30 is inserted into void 151 of receiver/sheath150, such that half of dowel 30 is located within void 151 (which issurrounded by concrete) and half of dowel 30 extends outward from sheath150 (not surrounded by concrete). A new slab of concrete is then pouredadjacent to the first slab such that the new concrete surrounds theexposed portion of dowel 30 protruding from sheath 150. Spacers 152,which are compressed against dowel 30, will prevent concrete from thesecond slab from entering void 151. The wet concrete is then vibrated toallow the concrete to consolidate around dowel 30.

FIG. 6 shows an alternative embodiment of dowel 30 having an elongatedshape. As is shown in FIG. 6, the elongated shape of dowel 30 allowsdeeper penetration into slabs 100 and 200 than the embodiment shown inFIGS. 3-5. FIG. 6 shows a situation in which dowel 30 is placed into apreexisting slab of concrete (slab 100); however, dowel 30 of FIG. 6 mayalso be used in connection with a sheath/receiver in the mannerdiscussed above. When the elongated dowel 30 of FIG. 6 is used in apreexisting slab, a deeper cutaway (120) is necessary than with thegenerally elliptical dowel of FIGS. 3-5, resulting in generally straightedges 125 of cutaway 120. As is shown in FIG. 6, dowel 30 includesrubber spacers 36 located toward the end of dowel 30 between edge 120 ofpreexisting slab 100, in addition to centering seals 35. Spacers 36provide additional support for the elongated dowel of FIG. 6;nevertheless, it will be appreciated that spacers 36 could be used withother dowel shapes, including those shown in FIGS. 3-5.

FIG. 7 shows another alternative embodiment of dowel 30 having agenerally rectangular elongated shape. Dowel 30 of FIG. 7 can include agenerally straight or flat end (39), or alternatively may include aslightly curved end to conform to the shape of the inner surface ofcutaway 120 of edge 110 of preexisting slab 100. The end of dowel 30opposite of end 39 can have a generally straight or flat shape since itwill be located in the newly poured slab (200).

In the foregoing description, certain terms have been used for brevity,clearness and understanding; but no unnecessary limitations are to beimplied therefrom beyond the requirements of the prior art, because suchterms are used for descriptive purposes and are intended to be broadlyconstrued. Moreover, the description and illustration of the inventionsis by way of example, and the scope of the inventions is not limited tothe exact details shown or described.

Although the foregoing detailed description of the present invention hasbeen described by reference to an exemplary embodiment, and the bestmode contemplated for carrying out the present invention has been shownand described, it will be understood that certain changes, modificationor variations may be made in embodying the above invention, and in theconstruction thereof, other than those specifically set forth herein,may be achieved by those skilled in the art without departing from thespirit and scope of the invention, and that such changes, modificationor variations are to be considered as being within the overall scope ofthe present invention. Therefore, it is contemplated to cover thepresent invention and any and all changes, modifications, variations, orequivalents that fall with in the true spirit and scope of theunderlying principles disclosed and claimed herein. Consequently, thescope of the present invention is intended to be limited only by theattached claims, all matter contained in the above description and shownin the accompanying drawings shall be interpreted as illustrative andnot in a limiting sense.

Having now described the features, discoveries and principles of theinvention, the manner in which the invention is constructed and used,the characteristics of the construction, and advantageous, new anduseful results obtained; the new and useful structures, devices,elements, arrangements, parts and combinations, are set forth in theappended claims.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

1. A dowel for connecting adjacent slabs comprising, a generally planarplate.
 2. The dowel as claimed in claim 1 further comprising a sealprotruding from said plate.
 3. The dowel as claimed in claim 2 whereinsaid seal comprises a rubber material.
 4. The dowel as claimed in claim1 wherein said plate is shaped to conform generally to the shape of acutaway in which the dowel is positioned.
 5. A saw unit for use in asystem of connecting slabs, said saw unit comprising: a saw blade; apositioning mechanism for aligning said saw blade along an edge of aslab; and an engaging mechanism for driving said saw blade into the edgeof the slab.
 6. The saw unit as claimed in claim 5 wherein saidpositioning mechanism comprises a vertical positioning mechanism foradjusting a height of said saw blade.
 7. The saw unit as claimed inclaim 5 wherein said positioning mechanism comprises an edge guidesensor.
 8. The saw unit as claimed in claim 5 wherein said engagingmechanism comprises an engagement cylinder associated with said sawblade.